Participants will have both vertical (up and down) and horizontal (side to side) saccadic eye movements measured at two time points before starting treatment with OGT 918 and after 12 months of treatment. For the test, patients sit in a chair with their head positioned as for a regular eye examination (steadied by a chin cup and headrest) and follow with their eyes a series of lights or laser spots moving on a screen at a distance of 1 meter (3 feet). During the test, patients wear either special recording glasses, infrared goggles, or special contact lenses for measuring eye movements. A full eye evaluation lasts about 1 hour, and each eye is evaluated twice. The evaluations are separated in time by at least an hour, and possibly a day.